SUMMARY. A key inflammatory output of the inflammasome, the proinflammatory cytokine interleukin-1beta (IL-1?), is one of the earliest and most important alarms to infection. Preliminary data by the candidate, Dr. Christopher LaRock, shows IL-1?-inhibiting immunotherapies for the treatment of autoinflammatory disease are associated with significantly increased reports of severe infections by group A Streptococcus (GAS). Through invasive infections like necrotizing fasciitis and complications like toxic shock syndrome, glomeruloronephritis, and rheumatic heart disease, GAS is one of the top ten causes of infection related mortality in the world. Yet comparatively mild infections like pharyngitis also make GAS one of the world's most common pathogens. Ultimately, the ability of GAS to invade tissue and cause the most severe diseases is limited by IL-1?; removal of this barrier with therapeutic anti-inflammatories thereby increases the risk of infection by GAS more so than for any other pathogen. While revealing a serious adverse effect that has a poor prognosis if not caught early, this observation also provides fundamental insights into molecular pathogenesis of GAS. That is, hyper-activation of IL-1? occurs independently of the inflammasome. Mechanistically, this occurs because the streptococcal protease SpeB can directly process IL-1? into a mature, signaling-competent form that establishes a hyper-inflammatory state. These findings therefore represent a paradigm where IL-1? and the inflammasome do not necessarily have overlapping functions in immunity. The research directions defined in this K22 proposal examine the biochemical activation of IL-1? by SpeB, the signaling activity that results, and how this inflammation controls GAS in murine models of invasive skin infection and pharyngitis. Understanding the molecular mechanisms involved gives insight into the pathogenesis of GAS that can lead to new therapeutic strategies, and insight into the inflammation that occurs during infections by several other leading bacterial pathogens. Accomplishing this requires a multi-pronged approach, benefiting from Dr. LaRock's graduate research on the inflammasome, and further developed during his tailored postdoctoral training that integrates animal models of infection, bacteriology of Gram-positive pathogens, and protease biochemistry. This K22 award provides the means to pursue this novel, important research direction and generate the preliminary data to support future junior faculty and R01 grant applications examining the molecular mechanisms of GAS pathogenesis and more broadly, the regulation of IL-1? during other diseases.